First of all, this is a very different Fenrir Greyback so I strongly recommend that you read his information here rather than assuming that he's similar to canon Fenrir. (Not that he won't end up like canon Fenrir but if so, it'll happen because of events in the game. He doesn't start out there.)
Basically, he was in Gryffindor and trained with axes. He went into the army and when he was twenty five he was bitten by a werewolf. He managed to kill that werewolf but the damage was done. He came back to Hogsmeade and Hogwarts but Dumbledore was absent (for plotty reasons no doubt!!) and corrupt people basically dismissed him from the army because they didn't want a werewolf in there. (Those damn snotty nobles.)
When Dumbledore returned, he tried to rectify the mistake but Fenrir refused to listen... because he was young, proud, an idiot Gryffindor and had a massive chip on his shoulder. So he didn't listen and left and wandered, picking up seasonal work when and where he could.
He's recently returned to Hogsmeade on the death of his parents and will quite likely find out that he's been a overly proud, stupid idiot fairly soon. :D Oh, and anyone who's been living in Hogwarts or Hogsmeade would likely know his father - his name was Hrafn Sigurdsson and he was a skald (which is an Icelandic bard - ostensibly they died out centuries ago but I think given the AU nature of this game we can say they persisted) - so they'd likely have heard him in the tavern or the inn, singing or telling grand epic poems and tales of war and warriors and gods and myths and so on and so forth.
Anyway, I'm rambling. Go and read his info and he's always available for plotty type stuff. (He'll also have more icons when I get home and can bulk upload them.)